Lida Ajer cave (Indonésie) : Early humans may have seen a supervolcano explosion up close

Early signs of human habitation in Lida Ajer cave on Sumatran (left) with an orangutan tooth for comparison

Two ancient teeth found in an Indonesian cave hint that our species had arrived there as early as 73,000 years ago – and may have had to deal with the biggest supervolcano eruption of the last few million years and also adapt to the challenges of living in thick rainforest.

Many archaeologists were puzzled by the recent discovery of 65,000-year-old stone tools and other artefacts in northern Australia. According to traditional thinking, early members of our species, Homo sapiens, were just beginning to venture out of Africa at this time.

To get from Africa to Australia, H. sapiens would also have needed to march across mainland Asia, then sail across the sea. The route should have included a stopover on the islands of Indonesia and Timor, but no H. sapiens artefacts older than 45,000 years had been found on these islands, until now.

Kira Westaway at Macquarie University in Sydney, Australia, and her colleagues have discovered that H. sapiensprobably did set foot in these islands more than 65,000 years ago.

The team took another look at two teeth dug up by Dutch archaeologist Eugène Dubois in Lida Ajer cave on the Indonesian island of Sumatra in the late 19th century. Partly through comparisons with orangutan fossils found nearby, they confirmed the teeth belong to our species – and using a modern dating technique known as electron spin resonance dating, they dated them between 63,000 and 73,000 years old.

“This is a significant finding because it supports emerging ideas that modern humans left Africa and reached Australia much earlier than we thought,” says Michelle Langley at Griffith University in Brisbane.

The discovery is also consistent with recent genomic analyses suggesting that our ancestors left Africa over 75,000 years ago and reached Indonesia more than 60,000 years ago.

Island challenges

But the archaeology hints that the first members of our species to reach Sumatra faced a tough life. They may have been present in Sumatra when the island’s now-dormant supervolcano – Toba – gave rise to one of Earth’s biggest known eruptions, perhaps about 71,000 years ago according to recent estimates.

If that didn’t wipe out the early population, they would have had to adapt to Sumatra’s rainforest environment – very different from the savannahs of Africa where humans evolved.

The lack of carbohydrate-rich plants and large animals for eating would have made survival difficult, says Westaway. “Successful exploitation of rainforest environments requires the capacity for complex planning and technological innovations.”

Then again, the tooth fossils are not proof of humans living in and exploiting the Sumatran rainforest, cautions Langley. Further research will be needed to find signs of habitation, such as cooking, tool or craft artefacts, she says. “It’s possible they were just passing through.”